Petrous apex chondrosarcoma

Findings

The head CT (bone windows) demonstrates a region of bony destruction extending from the right petro-occipital fissure into the carotid canal. The axial T2 images demonstrate a hyper intense, extra-axial, right petrous apex mass that extends from the petro-occipital fissure to the cavernous sinus. The margins of the mass are lobulated, and it encases the cavernous internal carotid artery. The axial T1 contrast-enhanced images demonstrate intense enhancement of the mass.


Diagnosis: Petrous apex chondrosarcoma


Key points

Classic MR imaging appearance of petrous apex chondrosarcoma is a mass located at the petro-occipital fissure with high T2 signal intensity that heterogeneously enhances.
The CT shows chondroid mineralization in 50%.
Invasive bone changes at the petro-occipital fissure strongly favors the diagnosis. Greater than 50% will have associated bone destruction.
2/3 located at the petro-occipital fissure, 1/3 located at the anterior basis sphenoid
Usually has lobulated margins
High T2 signal, low to intermediate T1 signal
Heterogeneous enhancement with contrast; whorls of enhancement within tumor matrix are often seen
Often displaces or encases the ICA
Classic presentation is a CN 6 nerve palsy. Other CN palsies can occur less commonly (3, 5, 7, 8—3, 4, and 6 are possible with cavernous sinus invasion)


Differential diagnosis
- Metastatic tumor
- Chondrosarcoma
- Plasmacytoma
- Nasopharyngeal cancer
- Chordoma
- Cholesteatoma
- Calcified meningioma
- Chondromyxoid fibroma

Distinguishing characteristics from other entities in the differential:
- Metastatic tumor – Can have a similar appearance; breast cancer and prostate cancer are two of the most common tumors to metastasize to the petrous apex
- Plasmacytoma - Usually intermediate T1 and T2 signal; usually more midline
- Chordoma - Similar appearance to chondrosarcoma but often see tumor "thumb" indenting the anterior pons; often midline
- Cholesteatoma - Does not enhance but has an otherwise similar appearance
- Calcified meningioma – Not typically destructive; low to intermediate T2 signal
- Chondromyxoid fibroma - Similar MR appearance to chondrosarcoma; areas of ground glass density can be seen on CT